The present invention relates to a contour vibration mode miniature quartz resonator, and more particularly to the cut angle, dimension, shape and electrode construction thereof.
It is an object of the present invention to miniaturize the resonator, to reduce the CI (crystal impedence), and to improve the frequency-temperature characteristics by suitably combining the cut angle, dimension, shape and electrode construction of the contour vibration mode quartz resonator.
It is another object of the present invention to provide a contour vibration mode miniature quartz resonator to be easily assembled.
Recently, electronization of a wrist watch has been advanced and particularly a quartz wrist watch incorporating a tuning fork type flexural quartz resonator as a frequency standard bus been put into a practical use. The frequency-temperature characteristics of the tuning fork type flexural quartz resonator is shown by a quadratic curve, and it is difficult to relize highly precise and stable frequency in a wide temperature range. Therefore, titanium acid barium condenser, the capacitance of which varies according to temperature, is employed for temperature compensation to thereby put the considerably high precision quartz wrist watch into a practical use. In this case, however, the precision of the quartz wrist watch is limited since the temperature compensation condenser should be adjusted to the temperature characteristic of the quartz resonator at the optimum value, and the capacitance of the temperature compensation condenser charges with the passage of time.
Therefore, an AT-cut quartz crystal wrist watch having a cubic frequency-temperature curve have been drawn an attention in order to improve the above mentioned disadvantages. As for the AT-cut quartz resonator, however, there are many spurious vibrations other than the thickness shear vibration used for the frequency standard, and the spurious vibrations injuriously affect on the various characteristics of the resonator. Accordingly, in order to separate the spurious vibrations from the major vibration (thickness shear vibration), the optimum dimension and the cut angle of the quartz crysal plate should be selected and exceedingly high precision is required. But the above requirements have not been achieved at present stage in the industrial view with respect to number of man-hour, yield and the like. Particularly, it is difficult to meet this requirement in the case of a miniature AT-cut quartz resonator for use in a wrist watch. Further, the supporting method which prevents a change of the spurious vibrations caused by support of the quartz resonator and a deteriotation of the CI and ensures sufficient shock resistance have not been proposed.
By the above mentioned various problems, the wrist watch incorporating therein the AT-cut quartz resonator as the frequency standard has scarcely been put into a market.
On the other hand, a GT-cut quartz resonator has also the cubic frequency-temperature curve, other than the AT-cut quartz resonator. The GT-cut resonator is scarcely used at present though it is conventionally used, but has never been used for a wrist watch.
For instance, the conventional GT-cut quartz crystal plate having the standard frequency of 100 KHz is considerably large in size, i.e., the long side, the short side and the thickness thereof are respectively 38.4, 32.9 and 3(mm), and further, since the cut angle of the GT-cut resonator is specific, the large rough stone is necessary and resultantly a cost of the GT-cut quartz crystal plate is very expensive. Moreover, since the GT-cut quartz crystal plate is large in size, the quartz crystal plate should have been supported by so called multi-points supporting method, i.e., the method to connect from 4 to 8 supporting wires fixed on from 2 to 4 portions (totaled 4 to 8 portions) on both surfaces on the nodal points of the quartz crystal plate taking the strength into account. Moreover, the solder balls are provided on the supporting wires at the positions where the leakage of vibration energy of the resonator is at minimum.
The multi-points supporting method will be shown in FIG. 1. As shown in FIG. 1, a quartz crystal plate 1 is supported by fixing one ends of supporting wires 2 such as headed wires and the like vertically and connecting the other ends of the supporting wires to supporting poles 3. Namely, silver points are fixed to the supporting positions of the quartz crystal plate 1 by burning and then the supporting wires 2 are vertically fixed to the silver points by providing conical solders 5a. The other ends of the supporting wires 2 are fixed to a substrate 6 and fixed to the supporting poles 3 being conductive to the external circuits by solders 5b. The supporting wires 2 should be adjustes so that the peaks of the conical solders 5a serve as nodes of vibration under the vibration frequency. Accordingly positions of solder balls 4 are adjusted in condition of FIG. 1 so that the peak of the conical solders serve as nodes of vibration of the supporting wires. This subtle and difficult process should be taken for all the supporting wires 2. Further, the elimination of the dimension of the GT-cut quartz resonator in the thickness direction is limited since there is a possibility that the conical solders are welded when the positions of the solder balls are adjusted, and thereby the excessive space is occupied. By way of an improvement of FIG. 1, a miniature GT-cut resonator having the long side, the short side and the thickness thereof respectively 8.03, 9.37 and 0.65(mm) is used to thereby reduce the number of the supporting wires.
The embodiment that the supporting wires of the quartz crystal plate is reduced will be shown in FIG. 2.
The method shown in FIG. 2 is completely the same as the method shown in FIG. 1 and each of the supporting wires 2 are fixed to the center of both surfaces of the quartz crystal plate 1. In this method even, though the number of the supporting wires is smaller than that of FIG. 1 and the adjustment of the solder balls have been simplified, the total occupied space has been reduced.
As illustrated above, the conventional supporting wire method of the quartz resonator as shown in FIGS. 1 and 2 has the following disadvantages; (1) the assembling process of the quartz resonator is troublesome and yield thereof is not good, (2) sufficiently large space is required, whereby the quartz resonator assembled by this supporting wire method could have never been applied to the wrist watches, since requirement of the quartz resonator incorporated into a wrist watch is the mass productivity and miniature size.
In order to improve upon the disadvantages of the supporting wire method, the vibrating portion and the supporting portion of the quartz resonator can be made in one piece as shown in FIG. 3. Namely the quartz crystal plate is easily supported and miniaturized by providing the supporting portion near the nodal line of the vibrating portion. In FIG. 3 a vibrating portion 11 and a supporting portion 12 are made in one piece by etching from a GT-plate. The long side, the short side and the thickness of the vibrating portion 11 are respectively 4.9, 4.2 and 0.04 (unit: mm) and the frequency thereof is 780 KHz. The supporting portion 12 is connected with the vibrating portion 11 near a nodal line 15 and fixed on the supporting member (not shown) at a portion 12 indicated by oblique lines. Simultaneously an electrode film 13a on the obverse surface and the electrode film 13b on the reverse surface of the vibrating portion 11 are conducted with the external circuit. Though this method is advantageous to the supporting wire method of FIGS. 1 and 2 with respect to a simple process and mass productivity, there is a room to miniaturize the supporting portion.
Namely, though the quartz crystal plate shown in FIG. 3 can be miniaturized than the quartz crystal plate shown in FIGS. 1 and 2, an excessive space is needed because of large supporting portion, whereby the quartz crystal plate shown in FIG. 3 is not suitable for use in a wrist watch. Further, since the vibration energy of the vibrating portion is transmitted to the supporting member even if the dimension and shape of the supporting portion is optimum, the leakage of vibration occurs and as a result, increase in CI, deterioration of pressure resistance and despersion in the frequency-temperature characteristics come out. On the other hand, the condition of the resilience coupling of the long side vibration and the short side vibration which controls controls characteristics of the GT-plate changes by the provision of the supporting portions, and as a result the characteristics of the quartz resonator change.